Recovery of oil from oil shale by underground hydrogenation



W. L. SLATER April 9, 1963 RECOVERY OF OIL FROM OIL SHALE BY UNDERGROUNDHYDROGENATION Filed Aug. s, 1960 SEH This invention relates to a methodfor in situ recovery of oil from naturally occurring deposits of oilshale. The process is particularly applicable to recovery of oil fromsubterranean deposits of oil shale. In accordance with the process ofthis invention, oil shale is hydrogenated in situ to liberate shale oilyand the hydrogen treated shale oil is then produced like crudepetroleum.

A number of proposals have been made for the recovery of oil fromunderground deposits of oil shale by heating the oil shale in place. Theoil shale may be heated by burning a portion of the shale oil or byburning an auxiliary fuel. By means of these in situ opera* tions, partof the potential Ioil content of the oil shale may `be recovered in theform of heavy hydrocarbon oil. Oil so recovered is extremely viscous andof very poor quality as compared with crude petroleum. When in situcombustion is employed for retorting the oil shale,

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a portion of the fuel value yof the shale, e.g. l0 to 30 percent, isconsumed as fuel in the burning operation.

The process of this invention provides for improved yields of shale oilof improved quality as compared with the retorting of oil shale. Inaccordance with the present hydrogenated in situ by contact withhydrogen at elevated temperature and pressure. The hydrogenationreaction which takes place in the oil shale form-ation produces a liquidproduct which is readily recoverable as a liquid hydrocarbon oil. Thecrude liquid product has a higher u API Gravity than oil produced fromthe same oil shale by conventional retorting operations. Heat requiredto raise the temperature of the oil shale formation to hydrogenationtemperature may be supplied by combustion of shale oil within the oilshale formation.

The accompanying ligure illustrates diagrammatically the method of oilrecovery from oil shale by in situ hydrogenation in accordance with thepresent invention.

The FIGURE, which illustrates a specific embodiment of this process,represents a vertical cross-section through a subterranean oil shaleformation.

With reference to the figure, an oil shale formation 2 is overlain bysubstantially impervious cap rock 3 and is underlain by substantiallyimpervious seam of bedrock 4. A plurality yof Wells are drilled from thesurface of the earth into the oil shale formation. As illustrated, wellbores 6 and 7 extend through the overburden to a point Iwithin the oilshale formation, preferably to a point near the lowermost portion of theoil shale formation. These Well bores are cased in the usual manner andprovided with tubing extending from the surface to la point within theoil shale formation near the bottom of the Well bore. The tubing strings8 and 9 are set in the well bores 6 and 7, respectively, in conformitywith good practice in the art of petroleum production.

To initiate the oil recovery operation, fuel and air are injectedthrough pipes 11 and 12 into well bore 6, Heavy hydrocarbon liquid issuitable as fuel, although some light liquid hydrocarbons, for example,gasoline, is desirable initially. Fuel may be introduced through pipe 11and tubing 8, or through pipe 12 and the annular passageway surroundingthe tubing in the well bore. Air is introduced to the well bore throughtubing 8. Initially, a charge of fuel is fed through tubing 8 to thebottom of the well bore Within the yoil shale formation. Then a ice flowof air is started through line 11 and tubing S. The fuel and air mix atthe lower end of tubing 8 forming a combustible mixture. Combustion isinitiated in the lower part of the well bore at the end of the tubingstring by suitable ignit-ing means, heating that portion of the oilshale formation surrounding the Well bore 6. Resulting products ofcombustion are discharged through annular space between the -wall of thewell bore and the tubing string to the surface of the earth. Outflow ofgas and pressure in the burning and producing zone are controlled byvalve 13. Additional fuel may be charged to the well through line 12.Gas discharged from the well bore may be combustible and can be used asfuel for preheating the hydrogen.

During the initial period of tiring, using an auxiliary fuel, thetemperature of the shale bed is raised to the desired temperature forsubsequent hydrogenation. Combustion is continued until the desiredtemperature has been reached, for example, 500 F. to 1500 F., in theshale surrounding the well bore. In some cases, after initial tiringwith auxiliary fuel, suicient oil from the oil shale will collect in theWell bore to permit combustion in the absence of the auxiliary fuel. Inthis case, the introduction of auxiliary fuel may be discontinued whilethe combustion-supporting gas, suitably air, is continuously supplied tothe well bore, burning a portion of the retorted oil and further heatingthe shale formation.

When the desired temperature, eg. 900 F., in the shale formation isreached, the introduction of air is disprocess, shale in an undergroundoil shale formation is '3: Continued At this time# 'air is Vented fromthe tubing and from the well bore through valve 14. Hydrogen from asuitable source is then supplied through line 15 and tubing 8 to the oilshale formation. Hydrogen is introduced into the formation, underpressure from compressor 16, until a pressure is reached within therange of about 1,000 to 5,000 pounds per square inch gauge, dependingupon the depth of the formation below the surface of the earth. Thehydrogen may be supplied directly to the well at pump dischargetemperature or may be preheated to a suitable temperature, e.g. 500 to1000* F., in heater 17. The -hydrogen is permitted to remain in contactwith the formation for a period of from about six hours to about twoweeks or longer. Additional hydrogen is furnished as necessary duringthis period to maintain the desired pressure. During the reaction periodoil is released from the oil shale and partially hydrogenated. Theresulting hydroretorted oil has improved properties, e.g. lowerviscosity and lower sulfur content, than conventionally retorted shaleoil. This oil accumulates in the Well bore. The oil may be periodicallyproduced through tubing string 8 by discontinuing the flow of hydrogenand permitting the oil to ow from the pressurized well bore through line18 to a suitable gas-oil separator 19. Gas separated from the oil may bepassed through line 21 to a gas holder 22 where it -is available forfurther use in the hydrogenation of the oil shale.

While retorting of oil shale and hydrotreating of the liberated shaleoil is taking place in Well bore 6, preheating of the oil shaleformation about well bore 7 is carried out by introduction of fuel andair to the well bore and initiating combustion therein as describedabove in connection with well bore 6. When sufficiently preheated,hydrogen separated from oil produced from well bore 6 may be introducedinto well bore 7 for -hydrotreating the subsurface oil shale formationsurrounding well bore 7.

When the rate of reaction between hydrogen and oil shale drops to animpractical low value, as indicated by the rate of pressure decline orrate at which hydrogen must be introduced into the formation to maintainreaction pressure (either of which may be determined at the surface),the introduction of hydrogen is stopped and the well depressured bypermitting gas and oil to flow from the well through tubing 8 (or 9),and through line 13 to separator 19. Following depressuring, theformation surrounding the. well `bore may be reheated by againintroducing air and fuel to. the well as described above. When reheatedto the desired temperature, for example, 500 to 1500 F., and purged ofair, hydrogen may Vbe again introduced through the well bore to theformation to effect further hydrogenation Iand recovery of oiltherefrom.

By providing a plurality of well bores, as illustrated in the ligure,the gas holder requirements may -be minimized or eliminated. With amultiplicity of wells, some wells may be in the preheat stage whileothers are in the pressuring, processing, or depressuring stages.Leakage or migration of oil and gas from one well to another is notdetrimental and is generally beneficial. When such leakage progresses tothe point where flow of gas is established from one well to the next,oil may be produced through the tubing string of one well at the sametime as hydrogen is introduced to the other. Also, when this conditionexists, the formation may be heated during the heating period by in situcombustion within the formation with either concurrent or countercurrentmovement of the ame front and the combustion air through the formationbetween communicating well bores. In situ combustion techniques are wellknown in the art.

Although only one set of well bores is illustrated in the drawing forthe purpose of illustration of the process of this invention, it is tobe understood that multiples may be employed in a suitable pattern, forexample, the iive spot or seven spot patterns well known in the art ofsecondary recovery from petroleum reservoirs.

Means other than direct combustion may be employed for supplying -heatto the oil shale formation, for example, by means of an electricalheater.

I claim: Y

1. A process for obtaining shale oil from a subterranean oil shalestratum penetrated by a well bore provided Ywith tubing extending fromthe surface of the earth into the oil shale formation, which comprisessupplying liquid hydrocarbon fuel to the bottom of said well bore withinthe oil shale formation, thereafter supplying air through said tubinginto contact with said liquid hydrocarbon fuel in the oil shaleformation and initiating combustion therein, withdrawing products ofcombustion from said oil shale formation through the annular spacebetween the wall of the well bore and the tubing while continuing thesupply of air thereto through said tubing effecting heating of said oilshale to a temperature within the range of about 500 to 1500 F.,discontinuing the introduction of air to said well bore, venting airfrom said tubing, introducing hydrogen through said tubing to the oilshale formation until a pressure is reached within the range of about1,000 to 5,000 pounds lper square inch gauge, permitting the hydrogen toremain in contact with the oil shale formation while maintaining saidpressure within said range for a period of at least 6 hours effectingrelease of shale oil from said oil shale and reaction between said shaleoil and hydrogen, and withdrawing liberated oil from said well bore.

2. A process according to claim 1 wherein hydrogen is introduced intothe well bore at a temperature within the range yof 500 to 1000" F.

3. A processk according to claim 1 wherein a plurality of spaced wellbores extending into said formation are employed and wherein preheatingof'oil shale formation surround-ing a first of said well bores iscarriedout simultaneously with hydrogen treatment of oil shale formationsurrounding a second of said well bores, the steps,y of discontinuingpreheating of oil shale formation surrounding said rst well bore,depressuring said second well bore by withdrawing hydrogen therefrom andsimultaneously supplying said withdrawn hydrogen to said preheated -rstwell bore. 'Y

References Cited in the file of this patent UNITED STATES PATENTS2,595,979 Pevere et al. May 6, 1952 2,847,306 Stewart et al Aug. 12,1958 2,970,826 Woodruif l Feb. 7, 1961

1. A PROCESS FOR OBTAINING SHALE OIL FROM A SUBTERRANEAN OIL SHALE STRATUM PENETRATED BY A WELL BORE PROVIDED WITH TUBING EXTENDING FROM THE SURFACE OF THE EARTH INTO THE OIL SHALE FORMATION, WHICH COMPRISES SUPPLYING LIQUID HYDROCARBON FUEL TO THE BOTTOM OF SAID 